In the third chapter, I focus on the concept of self-motion, which is tied to the definition of soul in Plato. Aristotle famously criticises this view in De anima 1.3, showing that the soul is unmoved. I offer the first lengthy discussion of Proclus’ repudiation of Aristotle’s criticism which differs from other Neoplatonist responses. Most importantly, I demonstrate how Proclus develops his own views on self-motion by using Platonic and Aristotelian insights.

The first chapter deals with Proclus’ little studied treatise Elements of Physics where he sums up in an axiomatic manner Aristotle’s theory of motion from Physics VI, VIII and De caelo I. I demonstrate that Proclus’ project is embedded in an exegetical tradition and show how he omits certain parts of Aristotle’s works that might conflict with his Neoplatonist views. Additionally, I provide evidence for the view that Aristotle’s Posterior Analytics proved to be influential for the axiomatic structure of Proclus’ treatise.

The second chapter concerns the origin of motion in the universe. While Plato assumes a self-moving soul as origin, Aristotle posits an unmoved intellect. Proclus brings these two views together by regarding the unmoved intellect as ultimate source of motion and the self-moving soul as an intermediary entity. I demonstrate that his harmonisation effort goes beyond previous Platonist attempts due to the philosophical reasoning he provides. I also defend Proclus’ assumption of both unmoved intellect and self-moving soul as sources of motion against concerns brought up in scholarship.

The goal of this study was to offer a wide-ranging treatment of Proclus’ engagement with Aristotle and his criticism of Plato by focusing on the concept of motion. Thematically, my results can be summed up in six areas.

(1) My main conclusion is that Proclus does not share the view of an essential agreement between Aristotle and Plato – contrary to what is sometimes assumed in scholarship. This emerges most clearly in Proclus’ discussion of Aristotle’s metaphysical system and specifically Aristotle’s rejection of the One as well as deficient understanding of the intellect’s causality (Chapter 4). Proclus regards Aristotle as a defective imitator and epigone of Plato. Aristotelian and Platonic metaphysics do not agree on the types of principles they recognise. As I argued, Proclus’ interpretation of Aristotelian metaphysics is more sensible than Ammonius’ et al. who vainly strive to find the Aristotelian equivalent to the Platonic One. Crucially, this insight has implications for the historiography of late antique philosophy: not all post-Porphyrian Neoplatonists adhere to the harmony-doctrine.

The fourth chapter examines the problem of the causality of the unmoved mover. This issue is central in scholarship on Aristotle and goes back to late antiquity. I argue that here Proclus’ non-harmonist stance towards Aristotle emerges most strongly: not only did Aristotle fail to make the intellect an efficient cause of the cosmos’ being but his metaphysics generally is deficient, since he did not recognise the Platonic One as the highest principle. I contrast Proclus’ view with the position of Ammonius and Simplicius who see a complete agreement between Plato and Aristotle.

In this introduction, I outline Proclus’ relationship with Aristotle and provide an overview of the state of the art. I discuss Proclus’ views on the so-called harmony of Plato and Aristotle and contrast it with the views of other, contemporary Neoplatonists, showing that Proclus stands out as more critical of Aristotle. I show that the concept of motion provides a perfect avenue for understanding how Proclus sees the tension between Plato and Aristotle. Lastly, I explain how Proclus differentiates distinct levels of motion which also structure my discussion in the monograph.

The chapter develops the question (raised in Chapter 4) about the precise way in which soul is supposed to play the role of the primary explanans of perception. It does so by bringing out the key difficulty that Aristotle faces and by analysing the three possible answers to this difficulty. The problem is that Aristotle seems to commit himself to three jointly inconsistent tenets: (i) the perceptive soul is the primary cause of perception; (ii) perception is passive; and (iii) the perceptive soul is impassive. These claims are inconsistent if it is true that (iv) there is no way for the soul of being the primary cause of φ-ing other than being the proper subject of whatever φ-ing consists in. Two dominant ways of resolving this problem, since antiquity, consist in denying Aristotle’s commitment to either (ii) or (iii). I argue that difficulties, both exegetical and philosophical, faced by each of these strategies are insurmountable. The third possible strategy starts from denying (iv). I trace such a strategy to the medieval idea of a sensus agens and argue that although the existing medieval (and later) versions cannot stand as such, the third strategy is nevertheless the most promising one.

The chapter explores how Aristotle wants to account for perception’s essentially receptive nature. It focuses on Aristotle’s commitment to the passivity of perception, namely, the idea that perception is a certain kind of being affected (paskhein) by perceptual objects. It provides a classification and preliminary critical analysis of existing interpretations of the passivity of perception. I argue that Aristotle’s first general account of perception in An. 2.5 is systematically pre-causal in the sense that makes it impossible to directly infer from it anything specific about the respective roles of the body and the soul (against both Material and Psychic Interpretation). Furthermore, I contend that Aristotle develops a robust conception of passivity here that successfully encapsulates, on the most general level, what perception is (against Deflationary and Aporetic Interpretation). More specifically, I argue that An. 2.5 is centrally aimed at reconciling perception’s passivity and completeness (the perceiver has both seen and is seeing the same object) and that this task is motivated by the need for capturing the difference between genuine (‘continued’) perceiving and mere appearance within an assimilation model of perception.

The chapter starts by outlining the version of direct realism endorsed by Aristotle. I argue that he was committed to uncompromised realism about perceptible qualities and to the view that we immediately perceive the bearers of these qualities without any need of further synthetic acts. These features highlight the difficulty of capturing the explanantia of perception. Two notions key to that endeavour are those of mediation and discrimination. The chapter provides a novel analysis of mediation (for discrimination, see Chapter 6), arguing that, for Aristotle, media are – more or less perfect – qualitative conductors. Furthermore, the chapter addresses the existing debate about what, according to Aristotle, happens in the sense organs when we perceive. I argue that the dilemma governing this debate between spiritualism and materialism (either ‘literalist’ or ‘analogical’) is a false one. Tertium datur, and this alternative turns out to be precisely the view Aristotle embraced: perception consists of a thoroughly material process, but what this process results in must not be a standing material likeness (which would mark the end of perception because like cannot be affected by like), but a dynamic ‘phenomenal’ likeness – the presence of a quality of the perceived object which remains to be precisely a quality of that object.